KR20230050387A - A Resource Saving Method for Zinc Phosphating Metal Surfaces - Google Patents

Abstract

The present invention relates to a method for zinc phosphating of a metal surface in a layer-forming manner using an aqueous colloidal solution as an activation step, wherein a zinc phosphate layer having a layer weight of less than 2.0 g/m ² is formed on the surface of zinc in a method step after activation. is formed on The activation step is based on a colloidal aqueous solution containing dispersed particulate components, which, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, are at least partially styrene and/or α with up to 5 carbon atoms. -containing a polymeric organic compound as a dispersant composed of olefins, the polymeric organic compound further comprising units of maleic acid, its anhydride and/or its imide, and the polymeric organic compound further comprising a polyoxyalkylene unit include In order to form a closed zinc phosphate coating that is sufficiently protected against corrosion and can be supplied for subsequent electrocoating, the aqueous colloidal solution needs to have a particulate content of at least 4 g/kg based on the aqueous colloidal solution.

Description

A Resource Saving Method for Zinc Phosphating Metal Surfaces

The present invention relates to a method for zinc phosphating of a metal surface in a layer-forming manner using an aqueous colloidal solution as an activation step, wherein a zinc phosphate layer having a layer weight of less than 2.0 g/m ² is formed on the surface of zinc in a method step after activation. is formed on The activation step is based on a colloidal aqueous solution containing dispersed particulate components, which, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, are at least partially styrene and/or α with up to 5 carbon atoms. -containing a polymeric organic compound as a dispersant composed of olefins, the polymeric organic compound further comprising units of maleic acid, its anhydride and/or its imide, and the polymeric organic compound further comprising a polyoxyalkylene unit include In order to form a closed zinc phosphate coating that is sufficiently protected against corrosion and can be supplied for subsequent electrocoating, the aqueous colloidal solution needs to have a particulate content of at least 4 g/kg based on the aqueous colloidal solution.

Layered phosphating is a method for applying crystalline anti-corrosion coatings to metal surfaces, especially materials of metallic iron, zinc and aluminum, which has been used for decades and studied extensively. The well-established zinc phosphating, especially for corrosion protection, is carried out at layer thicknesses of several micrometers and is based on the caustic pickling of metal materials in acidic aqueous compositions containing zinc ions and phosphates. In the process of pickling, an alkaline diffusion layer is formed on the metal surface, this layer extends into the interior of the solution and sparingly soluble crystallites are formed therein, which precipitate directly at the interface with the metal material. and continue to grow there. Water-soluble compounds, which are sources of fluoride ions, are often added to support the pickling reaction on metallic aluminum materials and to mask the bath poison aluminum, which in dissolved form hinders the formation of a layer on the metallic materials. do. Basically, zinc phosphating is set to achieve a closed crystalline coating at a layer weight of at least 2 g/m ² for good corrosion protection and coating primers, in particular on the zinc surface of the component. Depending on the metal surface to be phosphated, the concentration of the active ingredient in the pickling and zinc phosphating steps described above has to be adjusted accordingly in order to ensure a correspondingly high layer weight on the surface of metallic iron or steel, zinc and aluminum. Zinc phosphatization is always initiated by activation of the metal surface of the component to be phosphated. Wet-chemical activation is conventionally carried out by contact with a colloidal aqueous solution of phosphate ("activation step"), which, as long as they are immobilized on a metal surface, serves as a growth nucleus for the formation of a crystalline coating in the alkaline diffusion layer with subsequent phosphate used in fire Dispersions suitable in this case are colloidal, mainly neutral to alkaline aqueous compositions based on phosphate crystallites having only small crystallographic deviations in their crystalline structure from the type of zinc phosphate layer to be deposited. In this context, WO 98/39498 A1 teaches in particular divalent and trivalent phosphates of the metals Zn, Fe, Mn, Ni, Co, Ca and Al, wherein the phosphates of the metal zinc are used for activation for subsequent zinc phosphating. It is technically preferable to use

Activation steps based on dispersions of divalent and trivalent phosphates require a high degree of process control to keep the activation performance constant and at an optimal level, especially when processing a range of metal components. To ensure that this method is sufficiently robust, foreign ions carried over from previous treatment baths of colloidal aqueous solution or from the aging process should not cause deterioration of the activation performance. The deterioration is initially noticeable in layer weight increase in subsequent phosphating and ultimately results in the formation of a defective or non-uniform phosphate layer. Overall, therefore, layered zinc phosphating is a multi-step process that is technically complex to control and has so far been carried out in a resource-intensive manner both in terms of consumed energy and process chemicals. This applies in particular to the process step of zinc phosphating, which firstly requires high material requirements due to the formation of a layer on components with a zinc surface, but also requires a large amount of water into the phosphating bath in a manner linked to the required pickling rate. material removal. High pickling rates have the effect of requiring measures to prevent or prepare and dispose of phosphating sludge, which in turn requires the use of additional process chemicals.

Therefore, there is a need to optimize the pre-treatment line for zinc phosphating, including an activation step and a phosphating step, so that the whole process can be carried out in a less resource-intensive manner, especially in the pre-treatment of components with a zinc surface. there is. However, the whole resource-saving process must not sacrifice the properties of zinc phosphating, which is a homogenous material with high electrical charge transfer resistance in order to enable good protection against corrosion and correspondingly good coating of the coating in the subsequent electrocoating. and should be provided as a closed coating.

This complex working profile can surprisingly be achieved by the deposition of a relatively thin phosphate coating, requiring activation with a specific polymeric dispersant to stabilize the colloidal component of the activation step based on particulate phosphate, provided that a minimum amount of particulate matter is present. It is ensured that the component does not fall short of the activation step. Owing to the extremely efficient stabilization of the particulate components that lead to activation, certain dispersants ensure that high proportions of colloids can also be set up in the quasi-continuous process of zinc phosphation, which is surprisingly surprising for metal surfaces. leads to the formation of particularly thin but homogeneous closed phosphate coatings with improved activation of and high electroosmotic resistance.

The present invention therefore relates to a method for the anti-corrosion pretreatment of a metal material having at least partly a zinc surface, or of a component at least partly composed of such a metal material, in which the metal material or component is first activated (i) and then zinc phosphating (ii) in successive process steps, wherein the activation in process step (i) is carried out by contacting the metallic material or component with an aqueous colloidal solution, which comprises the dispersed particulate component of the solution (a ) at,

(a1) at least one particulate inorganic compound composed at least in part of phosphates of polyvalent metal cations selected from hopeeite, phosphophyllite, scholzite and/or hureaulite, and

(a2) at least one polymeric organic compound consisting at least in part of styrene and/or an α-olefin having up to 5 carbon atoms, said polymeric organic compound further comprising units of maleic acid, its anhydride and/or its imide; Containing the polymeric organic compound, wherein the polymeric organic compound further comprises a polyoxyalkylene unit;

the content of particulate components in the aqueous colloidal solution is at least 4 g/kg based on the aqueous colloidal solution;

A zinc phosphate layer having a layer weight of less than 2.0 g/m ² is deposited on the surface of the zinc in method step (ii).

In the context of the method according to the invention, a metallic material is made of zinc if at least one surface, to a material penetration depth of at least 1 micrometer, more than 50 atomic % of the metallic structure on this surface consists of zinc. do. It is a homogeneous material that is regularly applied to metallic materials consisting of more than 50 atomic % of zinc, but electrolytically galvanized or hot-dip galvanized which may also be alloyed with iron (ZF), aluminum (ZA) and/or magnesium (ZM). It also applies to materials provided with a metallic coating of zinc, such as strip steel.

The components processed according to the invention are in particular also semifinished products such as strips, sheets, rods, pipes and the like and composite structures assembled from said semifinished products (the semifinished products are preferably interconnected by gluing, welding and/or flanging). It can be a three-dimensional structure of any shape and design originating from the fabrication process, including complex structures).

In activation (i) of the process according to the invention, the dispersed particulate component (a) of the aqueous colloidal solution is retained by ultrafiltration of a defined partial volume of the aqueous dispersion with a nominal molecular weight cutoff (NMWC) limit of 10 kD. It is the solid content remaining after drying the water (retentate). Ultrafiltration is performed by adding deionized water (κ<1 μScm ⁻¹ ) until a conductivity of less than 10 μScm ⁻¹ is measured in the filtrate.

In the context of the present invention, an organic compound is polymeric if its weight average molar mass is greater than 500 g/mol. The molar mass is determined using a molar mass distribution curve of a sample of relevant reference values, which is experimentally established at 30° C. by size-exclusion chromatography using a concentration-dependent refractive index detector and, relative to a polyethylene glycol standard, corrected The average molar mass is evaluated computer-assisted according to the strip method using a cubic calibration curve. Hydroxylated polymethacrylate is suitable as a column material, and aqueous solutions of 0.2 mol/L sodium chloride, 0.02 mol/L sodium hydroxide, and 6.5 mmol/L ammonium hydroxide are suitable as eluents.

The method according to the present invention, when higher than the amount of particulate components of 4 g/kg in the colloidal aqueous solution, in the case of unusually lower layer weights, a homogeneous, closed zinc phosphate coating already grows on the surface of the metallic material, This surface is characterized by exhibiting a coating primer equivalent to prior art zinc phosphate coatings for subsequent electrocoating, while at the same time providing excellent coverage. In spite of this, the present invention provides, according to the present invention, that in method step (ii), a zinc phosphate coating having a layer weight of greater than 0.5 g/m ² , preferably greater than 1.0 g/m ² , is provided on the surface of the zinc. The aim is to deposit a homogeneous, closed zinc phosphate coating on the surface of the zinc, which is assumed to be

The reduction in layer weight also allows shorter wet chemical exposure times or contact times of zinc phosphating with the acidic aqueous composition, which in turn correlates with both lower pickling removal and overall shorter pretreatment duration. . A further reduction of the bed weight or contact time in zinc phosphating is achieved according to the invention, wherein the content of particulate components in the aqueous colloidal solution is at least 6 g/kg, particularly preferably at least 8 g/kg, more particularly preferably at least 10 g/kg. This can be achieved if the content of the particulate component in the aqueous colloidal solution is further increased so that the method is preferred. However, with a further increase in colloidal content in the activation step, the layer weight reduction achievable in zinc phosphatization is only marginal and further competes with the lower colloidal stability and disadvantages in process control in the activation step. Therefore, it is preferable to limit the content of the particulate component of the colloidal aqueous dispersion to 20 g/kg, particularly preferably to 15 g/kg, based on the aqueous colloidal solution in each case.

In the method according to the invention, the layer coating of zinc phosphate on the zinc surface should be limited to 2.0 g/m ² for resource-saving operation of the pre-treatment line. According to the present invention, due to the minimum amount of particulate components in the colloidal aqueous dispersion in the activation step, sufficiently homogeneous and closed zinc phosphate coatings with good coating behavior in the subsequent electrocoating are provided. Activation of the zinc surface is performed in method step (i) of the method according to the invention in such a way that a further reduction of the layer coating and thus a further reduction of material consumption in the zinc phosphating step in method step (ii) is possible. effective. It is therefore preferred to limit the layer weight of zinc phosphate on the zinc surface in method step (ii) to less than 1.8 g/m ² , particularly preferably less than 1.6 g/m ² and more particularly preferably less than 1.5 g/m ² . Limitation of the layer weight is achieved in process control through reduced contact time with the acidic aqueous composition for zinc phosphating in process step (ii) and/or by increasing the content of particulate components of the colloidal aqueous dispersion in process step (i). can be launched The layer weight of zinc phosphate is 5 wt% aqueous as a pickling solution that comes into contact with a defined area of phosphated material or component at 25° C. for 5 min immediately after zinc phosphating and washing with deionized water (κ<1 μScm ⁻¹ ). It is determined within the scope of the present invention by removing the zinc phosphate layer using % CrO ₃ and subsequently determining the phosphorus content in the same pickling solution by ICP-OES. The layer weight of zinc phosphate can be obtained by multiplying the amount of phosphorus relative to the surface area by a factor of 6.23.

A particular further advantage of the process according to the invention is that, in addition to zinc surfaces, iron and aluminum surfaces are also activated very effectively in process step (i) and, in process step (ii), are likewise very homogeneous and with a relatively low layer weight. A closed zinc phosphate coating is available on the surface. Thus, according to the invention, components which, in addition to zinc surfaces, also have iron and/or aluminum surfaces are preferably treated, with a layer weight of less than 2.0 g/m ² , particularly preferably less than 1.8 g/m ² , more particularly Preferably less than 1.6 g/m ² , and very particularly preferably less than 1.5 g/m ² , but preferably at least 0.5 g/m ² , particularly preferably at least 1.0 g/m ² , the zinc phosphate layer is preferably a method step ( In ii), a film is formed on the surface of iron and aluminum. Similarly, a metallic material is made of iron or aluminum if at least one surface is composed of iron or aluminum on which more than 50 atomic percent of the metallic structure is composed of iron or aluminum, to a material penetration depth of at least 1 micrometer.

Furthermore, condensed phosphates, which in the context of the present invention are soluble in water and are often added for colloidal stabilization in the activation step of prior art processes, are of only incidental importance in the context of the present invention to maintain consistently good phosphate coatings. It turned out that In the process according to the invention based on an activation step based on the particulate component (a), which is present in an amount of at least 4 g/kg based on an aqueous colloidal solution, the additivation of condensed phosphate may be omitted as a rule or completely. It is noteworthy and surprising to those skilled in the art that it can be. In a preferred embodiment of the method according to the invention, the content of condensed phosphate dissolved in the water in the activation step, based in each case on the element P, and based on the phosphate content of the at least one particulate compound in the aqueous colloidal solution, is less than 0.25 , particularly preferably less than 0.20, more particularly preferably less than 0.15 and very particularly preferably less than 0.10.

Also, preferably in this context, the content of the condensed phosphate dissolved in water in the aqueous colloidal solution of the method according to the present invention, calculated as P, is less than 100 mg/kg, particularly preferably less than 20 mg/kg, based on the aqueous colloidal solution, More particularly preferably less than 15 mg/kg, and very particularly preferably less than 10 mg/kg. Overall, in the context of the present invention, the addition of condensed phosphates can therefore be omitted entirely, so that activation, especially when processing a large number of components successively, takes place from a previous cleaning step involving the components to be pretreated to an activation step. contains only small amounts of condensed phosphates.

In the context of the present invention, condensed phosphates are metaphosphates and polyphosphates, preferably polyphosphates, particularly preferably pyrophosphates. Preferably the condensed phosphate is in the form of a compound of monovalent cations, preferably selected from Li, Na and/or K, particularly preferably from Na and/or K.

The content of condensed phosphate can be determined analytically from the difference in the total phosphate content in the non-particulate components of aqueous colloidal solutions with and without oxidative digestion, for example by peroxodisulphate, and the dissolved orthophosphate content can be measured photometrically. is quantified by Alternatively, when polyphosphates are used as condensed phosphates, enzymatic degradation using pyrophosphatase may occur instead of oxidative degradation. The non-particulate component of the aqueous colloidal solution is the solid content of the aqueous colloidal solution in the permeate of the ultrafiltration described above after being dried to a constant mass at 105°C - that is, the solid content after the particulate component (a) is separated by ultrafiltration.

The high tolerance of the method according to the invention against carried over foreign ions also enables the cleaning and rinsing steps carried out before the activation step and also the activation step itself to be performed with service water instead of deionized water. do. In this way, the method according to the invention is carried out in a particularly resource-saving manner. Thus, according to the present invention, the colloidal aqueous solution in the activation contains at least 0.5 mmol/L, particularly preferably at least 1.0 mmol/L, more particularly preferably at least 1.5 mmol/L of alkaline earth metal ions dissolved in water, but preferably It is preferable to contain at 10 mmol/L or less.

If the resistance of the method according to the invention is to reach system-specific limits in each case with an exceptionally high ionic strength, for example a high permanent water hardness and at the same time a high content of extraneous ions carried over from the previous cleaning step, long baths An organic complexing agent may be added to mask foreign ions to maintain life. In this case, it is necessary to evaluate the economic advantages of carrying out the activation step and whether, if necessary, the preceding cleaning step and rinsing with constant water are not hampered by the addition of the organic complexing agent and its technical monitoring in the system tank of the activation step. do. Suitable organic complexing agents preferred in this context are selected from α-hydroxycarboxylic acids, which in turn are preferably gluconic acid, tartronic acid, glycolic acid, citric acid, tartaric acid, lactic acid, very particularly preferably gluconic acid and/or selected from organophosphonic acids, which in turn are preferably selected from etidronic acid, aminotris(methylenephosphonic acid), aminotris(methylenephosphonic acid), phosphonobutane-1,2,4-tricarboxylic acid, diethylenetri aminepenta(methylenephosphonic acid), hexamethylenediamine tetra(methylenephosphonic acid) and/or hydroxyphosphonoacetic acid, particularly preferably etidronic acid.

In order to maintain a stable activating performance, the amount of the organic complexing agent in the aqueous colloidal solution is preferably not more than 2 times, particularly preferably not more than 1.5 times the amount of alkaline earth metal ions, very particularly preferably the amount of alkaline earth metal ions and It should be added only to an equimolar or lesser extent.

The aqueous colloidal solution in activation (i) of the process according to the invention preferably has an alkaline pH, particularly preferably a pH greater than 8.0, more particularly preferably greater than 9.0, but preferably less than 11.0, and has no effect on pH. The pH can be adjusted using a giving compound, such as phosphoric acid, sodium hydroxide solution, ammonium hydroxide or ammonia. "pH" as used in the context of the present invention corresponds to the negative decimal logarithm of the hydronium ion activity at 20 °C and can be determined by means of a pH-sensitive glass electrode.

For good activating performance, it is necessary to use multivalent metal cations in the form of phosphates which must be contained in the dispersed particulate component (a) for activation at correspondingly high proportions. Therefore, based on the dispersed particulate component (a) of the aqueous colloidal solution, the content of phosphate contained in the at least one particulate inorganic compound (a1) is preferably at least 25% by weight, particularly preferably at least 35% by weight, further It is particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight. The inorganic particulate component of the aqueous colloidal solution, in turn the particulate component (a) obtained from the drying of the ultrafiltration residue, is such that the infrared sensor gives the same signal (blank value) as the free CO ₂ carrier gas at the outlet of the furnace. It remains when it is pyrolyzed in a reactor with a CO ₂ oxygen-free flow at 900 °C without admixture of catalysts or other additives until it provides Phosphate salt contained in the inorganic particulate component is determined as phosphorus content by atomic emission spectroscopy (ICP-OES) immediately from acid decomposition, after acid decomposition of the component with a 10 wt % HNO ₃ aqueous solution at 25° C. for 15 minutes.

The active ingredient of the aqueous colloidal solution, which effectively promotes the formation of a closed phosphate coating on the metal surface and activates the metal surface in this sense, is, as already mentioned, composed mainly of phosphate, which in turn leads to the formation of a microcrystalline coating and Thus at least partly from hopate, phosphophyllite, sulzite and/or heurolite, preferably at least partly from hopate, phosphophyllite and/or sulzite, particularly preferably at least partly from hopate and /or from phosphophyllites and very particularly preferably at least partly from hopates. Activation within the meaning of the present invention is thus substantially based on the phosphate salt in particulate form contained in the activation step. Without taking water of crystallization into account, hopates stoichiometrically include Zn ₃ (PO ₄ ) ₂ and the nickel- and manganese-containing variants Zn ₂ Mn(PO ₄ ) ₃ , Zn ₂ Ni(PO ₄ ) ₃ On the other hand, phosphophyllite is composed of Zn ₂ Fe(PO ₄ ) ₃ , sulzite is composed of Zn ₂ Ca(PO ₄ ) ₃ , and heurolite is composed of Mn ₃ (PO ₄ ) ₂ . The presence of hopate, phosphophyllite, sulzite and/or heurolite in the crystalline phases in the aqueous dispersion according to the present invention is determined by ultrafiltration using a nominal molecular weight cutoff (NMWC) of 10 kD as described above. and separation of the particulate component (a) by drying the residue to constant mass at 105° C. followed by X-ray diffraction method (XRD).

Due to the preference for the presence of a phosphate containing zinc ions and having a certain degree of crystallinity, in the method according to the invention, for the formation of a firmly adhered crystalline zinc phosphate coating after successful activation, the colloidal aqueous dispersion is calculated as PO ₄ , at least 20% by weight, particularly preferably at least 30% by weight and more particularly preferably at least 40% by weight of zinc in the inorganic particulate component of the aqueous colloidal solution, based on the phosphate content of the inorganic particulate component.

However, activation in the sense of the present invention is preferably not achieved by means of a colloidal solution of titanium phosphate, since otherwise layered zinc phosphating on iron, in particular steel, would not reliably be achieved. In a preferred embodiment of the method according to the invention, the content of titanium in the inorganic particulate components of the aqueous colloidal solution is thus less than 0.01% by weight, particularly preferably less than 0.001% by weight, based on the aqueous colloidal solution. In a particularly preferred embodiment, the aqueous colloidal solution of the activation step (i) contains a total of less than 10 mg/kg, particularly preferably less than 1 mg/kg of titanium.

The activation step in the method according to the invention can be further characterized by its D50 value, above which the activation performance is significantly reduced. The D50 value of the colloidal aqueous solution is preferably less than 1 μm, particularly preferably less than 0.4 μm. In the context of the present invention, the D50 value refers to the particle diameter at which 50% by volume of the particulate components contained in the aqueous colloidal solution does not exceed. According to ISO 13320:2009, the D50 value is the volume-weighted cumulative particle size by scattered light analysis according to Mie theory immediately after sampling in the activation step using the refractive index of spherical particles and scattered particles of n _D = 1.52 - i 0.1 It can be determined at 20 °C from the distribution.

Within the meaning of the present invention, the polymeric organic compound (a2) used as dispersant consists partly of styrene and/or an α-olefin having 5 carbon atoms and maleic acid, its anhydride and/or its imide, It additionally contains polyoxyalkylene units. These polymeric organic compounds (a2) lead to extremely high stability of the aqueous colloidal solution in the activation step of the process according to the invention.

In this case the α-olefin is preferably selected from ethene, 1-propene, 1-butene, isobutylene, 1-pentene, 2-methyl-but-1-ene and/or 3-methyl-but-1-ene. selected, particularly preferably selected from isobutylene. It is clear to a person skilled in the art that the polymeric organic compound (a2) contains these monomers as structural units in unsaturated form covalently linked to each other or to other structural units. Representative suitable commercial ones are for example Dispex® CX 4320 (BASF SE), maleic acid-isobutylene copolymer modified with polypropylene glycol, Tego® Dispers 752 W (Evonik Industries AG), maleic acid modified with polyethylene glycol -styrene copolymers, or Edaplan® 490 (Muenzing Chemie GmbH), maleic acid-styrene copolymers modified with EO/PO and imidazole units. In the context of the present invention, preference is given to polymeric organic compounds (a2) which consist partially of styrene.

The polymeric organic compound (a2) used as dispersant is preferably 1,2-ethanediol and/or 1,2-propanediol, particularly preferably both 1,2-ethanediol and 1,2-propanediol. , and the content of 1,2-propanediol in the total polyoxyalkylene units is preferably at least 15% by weight based on the total polyoxyalkylene units, but particularly preferably 40 not exceed the weight percent. Also, the polyoxyalkylene unit is preferably contained in the side chain of the polymeric organic compound (a2). A content of polyoxyalkylene units in the total polymeric organic compound (a2) of preferably at least 40% by weight, particularly preferably at least 50% by weight, but preferably not more than 70% by weight is advantageous for dispersibility.

organic polymeric compounds ( a2) also has imidazole units, so that preferably the polyoxyalkylene units of the polymeric organic compound (a2) are at least partially end-capped with imidazole groups, so that in a preferred embodiment the terminal imidazole groups are polyoxyalkylene units. It is present in the alkylene side chain, and the covalent linkage of the polyoxyalkylene unit with the imidazole group is preferably carried out through a heterocyclic nitrogen atom.

In a preferred embodiment, the amine number of the organic polymeric compound (a2) is at least 25 mg KOH/g, particularly preferably at least 40 mg KOH/g, but preferably less than 125 mg KOH/g, particularly preferably 80 mg KOH/g, and thus in a preferred embodiment all of the polymeric organic compounds in the particulate component (a) also have this preferred amine number. The amine value is determined by weighing in each case about 1 g of the relevant reference value - the organic polymeric compound (a2) or all of the polymeric organic compounds among the particulate components - into 100 mL of ethanol, and the titration is carried out in an ethanol-based solution at 20 ° C. Titration is performed using a 0.1 N HCl solution against the indicator bromophenol blue until the color changes to yellow at a temperature of The amount of HCl titration solution used (in milliliters) multiplied by 5.61 divided by the exact mass of the weight in grams corresponds to the amine number in milligrams KOH per gram of the relevant reference value.

The presence of maleic acid can impart increased water solubility of the dispersant, especially in the alkaline range, insofar as it is a component of the organic polymeric compound (a2) as a free acid and not in the form of an anhydride or imide. Therefore, the polymeric organic compound (a2) in the particulate component (a), preferably also the polymeric organic compound as a whole, has an acid value according to DGF CV 2 (06) (April 2018) of at least 25 mg KOH/g , but preferably less than 100 mg KOH/g, particularly preferably less than 70 mg KOH/g, to ensure a sufficient number of polyoxyalkylene units. Further the polymeric organic compound (a2) of the particulate component (a), preferably also the polymeric organic compound as a whole, has in each case a hydroxyl value of 15, determined according to method A of 01/2008:20503 from European Pharmacopoeia 9.0. Preference is given to less than mg KOH/g, particularly preferably less than 12 mg KOH/g and more particularly preferably less than 10 mg KOH/g.

For sufficient dispersion of the inorganic particulate component in the aqueous colloidal solution, the content of the polymeric organic compound (a2) in the particulate component (a), preferably the entire polymeric organic compound, based on the particulate component (a), is at least 3 weight %, particularly preferably at least 6% by weight, but preferably not exceeding 15% by weight is sufficient.

In a preferred embodiment, the present invention relates to a method for pretreatment of corrosion protection comprising an aqueous dispersion. In this preferred process according to the invention, the aqueous colloidal solution in process step (i) is obtainable as an aqueous dispersion diluted by a factor of 20 to 100,000,

- as at least 5% by weight of the dispersed particulate component (A), based on the aqueous dispersion, in turn

(A1) at least one particulate inorganic compound consisting at least in part of phosphates of polyvalent metal cations selected from hopate, phosphophyllite, sholzite and/or heurolite;

(A2) at least one polymeric organic compound consisting at least in part of styrene and/or an α-olefin having up to 5 carbon atoms, said polymeric organic compound further comprising units of maleic acid, its anhydride and/or its imide; wherein the polymeric organic compound further comprises a polyoxyalkylene unit.

The dispersed particulate component (A) comprising, and

- optionally, preferably selected from urea urethane resins, particularly preferably urea urethane resins having an amine number of less than 8 mg KOH/g, preferably less than 5 mg KOH/g, particularly preferably less than 2 mg KOH/g , at least one thickener (B)

includes

For the dispersed particulate component (A) and at least one particulate inorganic compound (A1) and polymeric organic compound (A2) the same definitions and preferred specifications as given above for aqueous colloidal solutions apply.

Owing to the excellent colloidal stability of the particulate component (A) by the polymeric organic compound (A2) as a dispersant, the dilution is preferably carried out with deionized water (κ<1 μScm ⁻¹ ), particularly preferably constant, so that the present invention Make the method according to as resource-saving as possible. For fundamental technical applications, the constant contains at least 0.5 mmol/L of alkaline earth metal ions.

The presence of a thickener according to component (B), in combination with its particulate component in the aqueous dispersion, provides thixotropic flow behavior, thereby preventing the irreversible formation of agglomerates in the particulate component of the dispersion, from which primary particles cannot be detached. contribute to The addition of a thickener is such that the aqueous dispersion has a maximum dynamic viscosity at a temperature of 25° C. of at least 1000 Pa s, but preferably less than 5000 Pa s, in a shear rate range of 0.001 to 0.25 reciprocal seconds, preferably Preferably at a shear rate above that which exists at the maximum dynamic viscosity, it exhibits shear thinning behavior at 25° C., i.e. a decrease in viscosity with increasing shear rate, so that the aqueous dispersion as a whole can be preferably controlled to have thixotropic flow behavior. . The viscosity over the specified shear rate range can be determined in this case by means of a cone and plate viscometer with a gap width of 0.047 mm and a cone diameter of 35 mm.

The thickener according to component (B) is 0.5% by weight component in deionized water (κ<1 μScm ⁻¹ ) at a temperature of 25° C. at a shear rate of 60 rpm (= revolutions per minute) using a size 2 spindle. It is a polymeric chemical compound or defined mixture of chemical compounds having a Brookfield viscosity of at least 100 mPa·s. When measuring these thickener properties, the mixture is added to the water phase at 25° C. with agitation in the corresponding amount of the polymeric chemical compound and the homogenized mixture is then freed from air bubbles in an ultrasonic bath and allowed to stand for 24 hours, It must be mixed with water. The measured value of the viscosity is then read within 5 seconds immediately after application of a shear rate of 60 rpm by the second spindle.

The aqueous dispersions according to the invention preferably contain at least 0.5% by weight in total of one or more thickeners according to component (B), but preferably not more than 4% by weight, particularly preferably not more than 3% by weight, and The total content of polymeric organic compounds in the non-particulate components preferably also does not exceed 4% by weight (based on the dispersion). The non-particulate component is the solid content of the aqueous dispersion in the permeate of ultrafiltration described above after being dried to a constant mass at 105°C - that is, the solid content after the particulate component is separated by ultrafiltration.

Certain classes of polymeric compounds are particularly suitable thickeners according to component (B) and are also readily commercially available. In this regard, the thickeners according to component (B) are above all preferably selected from polymeric organic compounds, which in turn are preferably polysaccharides, cellulose derivatives, aminoplasts, polyvinyl alcohols, polyvinylpyrrolidone, polyurethanes and/or urea urethane resins, particularly preferably urea urethane resins.

Urea urethane resins as thickeners according to component (B) of the preferred process according to the invention for providing aqueous colloidal solutions starting from aqueous dispersions are polymeric compounds resulting from the reaction of polyhydric isocyanates with polyols and mono- and/or diamines. It is a mixture. In a preferred embodiment, the urea urethane resin is derived from polyhydric isocyanates, preferably 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2(4),4-trimethyl-1,6 -Hexamethylene diisocyanate, 1,10-decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 2,6-toluene diisocyanate, 2,4 -toluene diisocyanate and mixtures thereof, p- and m-xylylene diisocyanate, and 4-4'-diisocyanatodicyclohexylmethane, particularly preferably 2,4-toluene diisocyanate and/or m -xylylene diisocyanates. In a particularly preferred embodiment, the urea urethane resin originates from polyols selected from polyoxyalkylene diols, particularly preferably from polyoxyethylene glycols, which in turn preferably have at least 6, particularly preferably at least 8, more particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23 oxyalkylene units.

Urea urethane resins which are particularly suitable and thus preferred according to the invention are prepared by first reacting a diisocyanate, for example toluene-2,4-diisocyanate, with a polyol, for example polyethylene glycol, to obtain an NCO-terminated urethane prepolymer. formed and then further reacted with primary monoamines and/or primary diamines, for example m-xylylenediamine. A urea urethane resin having neither a free isocyanate group nor a blocked isocyanate group is particularly preferred. This urea urethane resin as a component of an aqueous dispersion obtainable by dilution of the aqueous colloidal solution of the process according to the invention promotes the formation of loose agglomerates of primary particles, which, however, are stabilized in the aqueous phase and in the aqueous dispersion are free from the particulate component. It is protected against further aggregation to the extent that sedimentation is largely prevented. To further enhance this property profile, a urea urethane resin having neither free or blocked isocyanate groups nor terminal amine groups is preferably used as component (B). In a preferred embodiment, the thickener according to component (B), which is a urea urethane resin, is thus in each case less than 8 mg KOH/g determined according to the method as described above for organic polymeric compounds (A2), particularly preferably It has an amine number of less than 5 mg KOH/g, more particularly preferably less than 2 mg KOH/g. The thickener substantially dissolves in the aqueous phase and can thus be assigned to the non-particulate components of the aqueous dispersion, whereas component (A2) is substantially bound to the particulate component (A), so that all of the polymeric organic compounds of the non-particulate components Preference is given to aqueous dispersions for providing activated, colloidal aqueous solutions having an amine number, preferably less than 16 mg KOH/g, particularly preferably less than 10 mg KOH/g and more particularly preferably less than 4 mg KOH/g. It is also preferred that the urea urethane resin has a hydroxyl number in the range of 10 to 100 mg KOH/g, particularly preferably 20 to 60 mg KOH/g, determined according to method A of 01/2008:20503 from the European Pharmacopoeia 9.0 do. Regarding molecular weight, urea urethane resins in the range from 1000 to 10000 g/mol, preferably from 2000 to 6000 g/mol, determined experimentally in each case, as described above in connection with the definition according to the invention of polymeric compounds. A weight average molar mass of is advantageous according to the present invention and is therefore preferred.

Without the addition of auxiliaries, the pH of the dispersion to give the aqueous colloidal solution of the activation of the process according to the invention is generally in the range 6.0-9.0, and therefore this pH range is preferred according to the invention. However, for compatibility with practical and regular aqueous alkaline colloidal solutions in the activation step, it is advantageous for the pH of the aqueous dispersion to be greater than 7.2, particularly preferably greater than 8.0, if necessary as a result of the addition of compounds which react in an alkaline manner. do. Since some polyvalent metal cations have an amphoteric character and can therefore be desorbed from the particulate component at higher pH values, the alkalinity of the aqueous dispersion according to the present invention is ideally limited, such that the pH of the aqueous dispersion is preferably less than 10, and particularly preferably less than 9.0.

Aqueous dispersions as described above to give aqueous colloidal solutions are as such preferably obtainable by

i) 10 parts by mass of an inorganic particulate compound (A1) is ground together with 0.5 to 2 parts by mass of a polymeric organic compound (A2) in the presence of 4 to 7 parts by mass of water, 1000 diluting with water by a factor of two and then grinding until the D50 value, determined by dynamic light scattering, is less than 1 μm to give a pigment paste;

ii) at least 5% by weight of the dispersed particulate component (A) and water in such an amount that a maximum dynamic viscosity of at least 1000 Pa s is established at a temperature of 25 ° C in a shear rate range of 0.001 to 0.25 reciprocal seconds, preferably deionized diluting the pigment paste with ionized water (κ<1 μScm ⁻¹ ) or a constant and a thickener (B); and

iii) setting a pH in the range of 7.2 to 10.0 using a compound that reacts in an alkaline manner;

Preferred embodiments of the dispersion are similarly obtained by selecting the corresponding components (A1), (A2) and (b) in each case as needed or in the required amounts, as described in relation to aqueous colloidal solutions. .

The aqueous dispersions may also contain auxiliaries, for example selected from preservatives, wetting agents and antifoaming agents, which are contained in the amount required for the function concerned. The content of other compounds in the non-particulate components that are not auxiliaries, particularly preferably thickeners and which are not compounds that react in an alkaline manner, is preferably less than 1% by weight. In the context of the present invention, compounds which react in an alkaline manner are water soluble (water solubility: at least 10 g per kg of water with κ<1 μScm ⁻¹ ) and have a pK _B value greater than 8.0 for the first protonation step. have

The resource-saving method control according to the invention is particularly effective in the case of zinc phosphating of components continuously, ie during operation of a pretreatment line for zinc phosphating. In a preferred embodiment of the method according to the invention, a number of specific components consisting at least partly of a metallic material, at least one surface of which is zinc, are therefore processed successively. A series of pretreatments is when, according to the invention, a series of components are each first activated and then zinc phosphated and brought into contact with a bath for activation and zinc phosphating provided for this purpose in a system tank, the individual components in turn being They come into contact in turn and thus at different times. In this case, the system tank is a vessel in which a colloidal aqueous solution is placed for activation purposes or an acidic aqueous composition is placed for phosphorylation purposes.

A rinsing step may be present between activation (i) and zinc phosphating (ii) to reduce carryover of the alkaline components into the acidic aqueous composition for zinc phosphating, but the rinsing step preferably completely removes the activation of the metal surface. omitted to retain The rinsing step is performed by removing the metal-element-based or semi-metal-element-based active ingredients already consumed by simply contacting the metal surface of the component with the rinsing liquid, from the component being treated, without being contained in the rinsing liquid itself. It is used exclusively for the complete or partial removal of soluble residues, particles and active components carried over by adhering to the components from the wet-chemical processing step of the process. For example, the rinse liquid may simply be tap or deionized water, or, if desired, may also be a rinse liquid containing a surface-active compound to improve wettability by the rinse liquid.

For the purpose of activating the metallic material, for layer-forming zinc phosphating and formation of a semi-crystalline coating, amounts of 5-50 g/L of phosphate ions, 0.3-3 g/L of zinc ions and free fluoride are used. Phosphating in process step (ii) by contacting the surface with an acidic aqueous composition containing According to the present invention, the amount of phosphate ions includes orthophosphoric acid and anion dissolved in water of a salt of orthophosphoric acid, calculated as PO ₄ .

The amount of free fluoride or the source of free fluoride ions comprises surfaces of iron or aluminum as well as surfaces of zinc, as required, for example for zinc phosphating of motor vehicle bodies which are at least also partly made of aluminum. It is essential to the process of layered zinc phosphating insofar as the components that do so are zinc phosphated in a layered manner. In this context, it is advantageous if the amount of free fluoride in the acidic aqueous composition is at least 0.5 mmol/kg, particularly preferably at least 2 mmol/kg. The concentration of free fluoride must not exceed a value above which the phosphate coating has predominantly easily washable adhesion, which adhesion is to be avoided even by a disproportionately increased amount of particulate components in the colloidal aqueous solution of the activator. because it can't Thus, in the process according to the invention based on activation (i) followed by zinc phosphating (ii), the concentration of free fluoride in the acidic aqueous composition of zinc phosphating is less than 15 mmol/kg, particularly preferably 10 mmol/kg Less than kg and more particularly preferably less than 8 mmol/kg are economically advantageous and therefore preferred.

The amount of free fluoride can be determined potentiometrically by means of a fluoride-sensitive measuring electrode at 20° C. in the relevant acidic aqueous composition after calibration with a fluoride-containing buffer solution without pH buffering. Suitable sources of free fluoride ions are hydrofluoric acid and its water-soluble salts, such as ammonium bifluoride and sodium fluoride, and complex fluorides of the elements Zr, Ti and/or Si, in particular of the element Si. In the phosphating process according to the invention, the source of free fluoride is thus preferably selected from hydrofluoric acid and its water-soluble salts and/or complex fluorides of the elements Zr, Ti and/or Si. A salt of hydrofluoric acid is water soluble within the meaning of the present invention if its solubility in deionized water at 60° C. (κ<1 μScm ⁻¹ ) is at least 1 g/L, calculated as F.

In those processes according to the present invention wherein zinc phosphating is performed in step (ii), to inhibit what is known as “pin-holing” on the surface of a metallic material made of zinc, the source of free fluoride is It is preferably selected at least partially from complex fluorides of the element Si, in particular from hexafluorosilicic acid and salts thereof. The term pin-holing refers to the phenomenon of local deposition of an amorphous, white zinc phosphate in an otherwise crystalline phosphate layer on a treated zinc surface or on a treated galvanized or alloy-galvanized steel surface. It is understood by those skilled in the art of phosphating.

In process step (ii) of the process according to the invention, the preferred pH of the acidic aqueous composition is greater than 2.5, particularly preferably greater than 2.7, but preferably less than 3.5 and particularly preferably less than 3.3. The content of free acid to the point in the acidic aqueous composition of the zinc phosphating in process step (ii) is preferably at least 0.4, but is preferably at most 3.0, particularly preferably at most 2.0. The percentage of free acid as a point is determined by diluting a sample volume of 10 mL of the acidic aqueous composition to 50 mL and titrating to a pH of 3.6 with 0.1 N sodium hydroxide solution. The consumption of mL of sodium hydroxide solution represents the point number of the free acid.

The conventional addition of additives for zinc phosphating can also be carried out similarly in the context of the present invention, such that the acidic aqueous composition in process step (ii) is a conventional accelerator such as hydrogen peroxide, nitrite, hydroxylamine , nitroguanidine and/or N-methylmorpholine-N-oxide and additionally cations of metal manganese, calcium and/or iron in the form of water-soluble salts, which have a positive effect on layer formation. An embodiment in which the acidic aqueous composition for zinc phosphating in process step (ii) contains less than 10 ppm in total of nickel and/or cobalt ions is particularly preferred from an ecological point of view.

In the method according to the invention, a good coating primer for subsequent dip coating is prepared substantially in the course of which an organic cover layer is applied. Thus, in a preferred embodiment of the method according to the invention, zinc phosphating is carried out with or without an intermediate rinse and/or drying step, but preferably with a rinse step and without a drying step, followed by dip coating, particularly preferably This is followed by an electrocoating, more particularly preferably a cathodic electrocoating, which preferably contains, in addition to the dispersed resin, a water-soluble or water-dispersible salt of yttrium and/or bismuth, which is preferably an amine-modified polyepoxide. includes

Claims (14)

A method for anti-corrosion pretreatment of a metallic material having at least partly a zinc surface or of a component consisting at least partly of said metallic material, comprising the steps of:
In the method, the metallic material or component is first subjected to activation (i) and then zinc phosphating (ii) in successive method steps, wherein the activation in method step (i) transforms the metallic material or component into a colloid. carried out in contact with an aqueous solution, wherein said aqueous colloidal solution, in the dispersed particulate component (a) of said solution,
(a1) at least one particulate inorganic compound composed at least in part of phosphates of polyvalent metal cations selected from hopeeite, phosphophyllite, scholzite and/or hureaulite, and
(a2) at least one polymeric organic compound at least partially composed of styrene and/or an α-olefin having up to 5 carbon atoms, said polymeric organic compound further comprising maleic acid, its anhydride and/or its unit, and the polymeric organic compound further contains a polyoxyalkylene unit,
the content of particulate components in the aqueous colloidal solution is at least 4 g/kg based on the aqueous colloidal solution;
A method for anti-corrosion pretreatment, wherein a layer of zinc phosphate having a layer weight of less than 2.0 g/m ² is deposited on the surface of the zinc in method step (ii). According to claim 1,
In said aqueous colloidal solution, the content of condensed phosphate dissolved in water is less than 0.25, preferably less than 0.20, particularly preferably less than 0.20, in each case based on element P and based on the phosphate content of said at least one particulate compound. A method for anti-corrosion pretreatment, characterized in that it is less than 0.15, more particularly preferably less than 0.10. According to one or both of claims 1 to 2,
A method for anti-corrosion pre-treatment, characterized in that said aqueous colloidal solution in said activation (i) has an alkaline pH, preferably greater than 8.0, particularly preferably greater than 9.0, but preferably less than 11.0. According to one or more of claims 1 to 3,
The content of phosphate, calculated as PO ₄ , contained in the at least one particulate inorganic compound (a1) is preferably at least 25% by weight, particularly preferably at least 25% by weight, based on the dispersed inorganic particulate components of the aqueous colloidal solution. at least 35% by weight, more particularly preferably at least 40% by weight and very particularly preferably at least 45% by weight. According to one or more of claims 1 to 4,
The polymeric organic compound (a2) of the aqueous colloidal solution contains polyoxyalkylene units in its side chain, and the content of polyoxyalkylene units in the entirety of the polymeric organic compound (a2) is preferably at least 40% by weight; Method for anti-corrosion pretreatment, characterized in that it is particularly preferably at least 50% by weight, but particularly preferably does not exceed 70% by weight. According to one or more of claims 1 to 5,
The organic polymeric compound (a2) of the aqueous colloidal solution also preferably has imidazole units, preferably in such a way that the polyoxyalkylene units of the polymeric organic compound (a2) are at least partially end-capped with imidazole groups. A method for a characterized corrosion protection pretreatment. According to one or more of claims 1 to 6,
The aqueous colloidal solution is preferably from a urea urethane resin, preferably from a urea urethane resin having an amine number of less than 8 mg KOH/g, particularly preferably less than 5 mg KOH/g and very particularly preferably less than 2 mg KOH/g Process for anti-corrosion pretreatment, characterized in that it contains as further component b) at least one selected thickener. According to one or more of claims 1 to 7,
based on the particulate components of the aqueous colloidal solution and of which the total polymeric organic compounds account for at least 3% by weight, preferably at least 6% by weight, but preferably not more than 15% by weight. way for. According to one or more of claims 1 to 8,
The method for anti-corrosion pretreatment, characterized in that the colloidal aqueous solution has a D50 value of less than 1 μm, preferably less than 0.4 μm. According to one or more of claims 1 to 9,
The content of particulate components of the aqueous colloidal solution is at least 6 g/kg, preferably at least 8 g/kg, particularly preferably at least 10 g/kg, but preferably not more than 20 g/kg, in particular based on the aqueous colloidal solution in each case. Method for anti-corrosion pre-treatment, characterized in that it is preferably not more than 15 g / kg. According to one or more of claims 1 to 10,
The colloidal aqueous solution can be obtained as an aqueous dispersion diluted 20-fold to 100,000-fold,
- at least 5% by weight of the dispersed particulate component (A), based on the aqueous dispersion, in turn
(A1) at least one particulate inorganic compound composed at least partially of phosphates of polyvalent metal cations selected from hopate, phosphophyllite, schollzite and/or heurolite;
(A2) at least one polymeric organic compound at least partially composed of styrene and/or an α-olefin having up to 5 carbon atoms, said polymeric organic compound further comprising maleic acid, its anhydride and/or its unit, and the polymeric organic compound further comprises a polyoxyalkylene unit.
The dispersed particulate component (A) containing
- optionally, preferably selected from urea urethane resins, particularly preferably from urea urethane resins having an amine number of less than 8 mg KOH/g, preferably less than 5 mg KOH/g, particularly preferably less than 2 mg KOH/g at least one thickener
A method for anti-corrosion pre-treatment comprising a. According to one or both of claims 1 to 11,
characterized in that a zinc phosphate layer having a layer weight of less than 1.8 g/m ² , preferably less than 1.6 g/m ² and particularly preferably less than 1.5 g/m ² is deposited on the surface of the zinc in process step (ii). Methods for anti-corrosion pre-treatment. According to one or more of claims 1 to 12,
The zinc phosphatization in process step (ii) comprises 5-50 g/kg of phosphate dissolved in water, 0.3-3 g/kg of zinc ions, calculated as PO ₄ , and less than 0.1 g/kg of elements in total. A method for an anti-corrosion pretreatment, characterized in that it is carried out by contact with an acidic aqueous composition containing an amount of free fluoride which may also contain ions of nickel and cobalt. According to one or more of claims 1 to 13,
In addition to the zinc surface, also components with an iron and/or aluminum surface are treated, with a layer weight of less than 2.0 g/m ² , particularly preferably less than 1.8 g/m ² , more particularly preferably less than 1.6 g/m ² , and very particularly preferably a zinc phosphate layer of less than 1.5 g/m ² is preferably deposited on all surfaces of zinc, iron and aluminum in process step (ii).